1. Field of the Invention
The present invention relates to a liquid crystal display device having a liquid-crystal layer sandwiched between one pair of substrates.
2. Description of the Related Art
In Patent Documents 1, 2, and 3 listed below, a scheme with comb-like electrodes provided on one substrate is proposed as a scheme in which an electric field is applied to a liquid crystal on the substrate horizontally. This scheme is hereinafter referred to as the horizontal field scheme or in-plane switching (IPS) mode. In this scheme, the liquid-crystal molecules rotate in a parallel plane with respect primarily to the substrate. It is known, therefore, that a wide viewing angle can be obtained since, when the crystal is viewed obliquely, the difference in birefringent index between the application of the electric field and non-application thereof is insignificant.
At the same time, it is also seen that in the IPS mode, although changes in the birefringent index of the crystal itself are insignificant, the characteristics of polarizers cause light to leak when the crystal is viewed from the azimuthally oblique directions shifted from the absorption axes of the polarizers. A scheme that employs retardation films to prevent such leakage of light from the oblique directions of polarizers is disclosed in Patent Document 4. In this document, however, although consideration is given to reducing the influence of the liquid crystal in a vertical alignment (VA) mode by improving only the viewing angles of the polarizers, no description is given of compensating for the influence of the liquid-crystal layer in the IPS mode.
In Patent Document 5, while a means for solving the problem that white changes in color according to the particular viewing direction is disclosed, the improvement of black display characteristics is not described.
Meanwhile, a configuration with a retardation film disposed inside one of multiple polarizers in order to improve the viewing angle characteristics of black display is disclosed in Patent Document 6. This scheme also allows for the influence of the triacetylcellulose (TAC) disposed as a supporting base material on both sides of the polarizer. It has been found during the present inventors' studies, however, that the configuration with one phase compensator at one side does not merely cause black to sink sufficiently, but does not reduce changes in color due to the wavelength dispersion of the liquid-crystal layer, either. In addition, the difference in phase compensation due to whether the alignment axis (slow axis) of the liquid-crystal molecules during black display is parallel or perpendicular to the absorption axis of the polarizer at the incident side is not described in Patent Document 6. In the known examples described above, the viewing angle characteristics are discussed in terms of luminance characteristics only and no measures against the color change are disclosed.
Furthermore, a configuration that includes substantially an optically isotropic supporting base material in one polarizer and a retardation film in another polarizer in order to improve the oblique luminance disturbance and/or oblique color disturbance of black display is disclosed in Patent Document 7. The present inventors have studied this scheme to find that although the scheme makes it possible to eliminate the influence of the wavelength dispersion of a liquid-crystal layer, the display device itself is not constructed to reduce changes in color due to the wavelength dispersion of a retardation film.    Patent Document 1: JP-B-S63-21907    Patent Document 2: JP-A-H09-80424    Patent Document 3: JP-A-2001-056476    Patent Document 4: JP-A-2001-350022    Patent Document 5: Japanese Patent No. 3204182    Patent Document 6: Japanese Patent No. 2982869    Patent Document 7: JP-A-2005-208356    Patent Document 8: JP-A-2005-3733    Non-Patent Document 1: “Crystal Optics”, compiled by the Japan Society of Applied Physics, KOUGAKU-KONWAKAI, published by Morikita Publishing Co., Ltd., 1984, 1st Edition, 4th Print, Chapter 5, pp. 102-163    Non-Patent Document 2: “Fundamental Engineering”, Gendaikougakusha, 1999, 3rd Edition, Chapter 4, p. 210    Non-Patent Document 3: J. Opt. Soc. Am. paper entitled “Optical in Stratified and Anisotropic Media: 4×4-Matrix Formulation”, written by D. W. Berreman, 1972, Volume 62, No. 4, pp. 502-510